Univention Corporate Server 4.0 erratum 124 (bugfix)

This update addresses the following issues:
* The Univention Configuration Registry (UCR) variable descriptions for
"mail/localmailboxsizelimit" and "mail/messagesizelimit" have been
updated as "0" does not implement "unlimited" as previously mentioned.
* Additional arguments for smtpd processes may now be added via UCR
variables. The given arguments are automatically added to the config
file /etc/postfix/master.cf. The following UCR variable prefixes are
currently supported:
- mail/postfix/mastercf/options/smtp/...
- mail/postfix/mastercf/options/smtps/...
* The first changes to the main.cf framework have been done for defining
a custom restriction rule set via UCR variables for Postfix' smtps
port (465). There is currently no change in Postfix behaviour.